Resistance controller



July 4, 1933. E. w. S-EEGER 1,916,534

RES I STANCE CONTROLLER Filed June '7, 1929 I N V EN TOR.

his" B fiwmwmm A TTORNEY Patented July 4, 1933 UNITED STATES PATENT crrlcr.

EDWIN W. SEEG-EB, OF WAUWATOSA, WISCONSIN, ASSIGNOR TO CUTLER-HAMMER, -INC., OF MIll'jiFfA'UKEE, WISCONSIN, A CORPORATION OF DELAWARE nnsrsrancn conrnonnnn Application filed June '7,

This invention relatesto controllers for electric circuits and more particularly to the control of resistancesfor gradual inclusion in and exclusion from such circuits. v, The invention is particularly applicable to the control of dynamo electric machines by means of resistances in their armature circuits.

In certain motor installations, for instance in drives for fans and blowers, it is desirable to provide a large number of speed points for the motors. The ordinary arrangement of resistances and controllers for such an installation would require an excessive number of resistance sections and a correspondingly large number of contacts on the controller, resulting in a large controller, the cost of which may be prohibitive. Furthermore, when the motor to be controlled is of large capacity, the contacts on the controller and the wires connecting the controller and resistance sections have to be of such large capacity, that the controller will be prohibitive in size and ditficult of manipulation, and

the accommodation of the connecting wireswill be another serious problem. 1 i

If the controller is of the type where the resistance is commutated by magnetic switches, which in turn are controlled by a master controller, the number and size of the switches required to obtain alarge number of resistance steps may be prohibitive.

Moreover such large magnetic switches" have a highly inductive magnet circuit, which results in rapid wear due'to burning of the contacts of the master controller,

If a system of control in which a limited number of resistance sections and corresponding switches, is employed, the various sections may be cut in and out of circuit in various combinations, thereby yielding a relatively greater number of possible speed points. But this system has the disadvantage that the opening and-closing of the respective magnet operating circuits, when changing from one'combination to another, does not take place coincidently, so that undesired intermediate combinations result, which interfere with the smooth operation of the motor.-

An object-of my invention is to provide a 1929. Serial No. 369,096.

stantially instantaneously.

7 Another ob] set is the elimmation of spark i ing at the master controller due to the com mutation of the resistances or switches. Another: object is to provide a controller of the'aforedescribed kind in which undesired; resistance stepping during commutation is avoided. a V

Another object is to provide a controller in which the speed of change-over between successive points of the controller is independcnt'of the speed'with which the master is moved between successive points. Further objects and advantages vcntion willhereinafter appear.

The single figure of the accompanying drawing illustrates schematically and diagrammatically one embodiment of my invention, which will now be described, it being understood, that the invention is susceptible of embodiment in other forms without departing from the scope of the appended claim.

Referring to the drawing, A represents the armature and F the series field of a direct current motor, which is supplied with energy from the lines L1 and L The current to the motor is controlled by means of resistance steps R R R and R The resistances R to one ohm. V

of the iny R are so'propor tioned, that the ratio of their ohmic values The motor circuit :is closed by means of the mainswitchMa, which is equipped with an clectromagnet M," the latter when energized causing closure of the switch. The-rcsistances R to R are controlled by the respective resistance commutating electromag- 'nctic switches 1a to 4a, the switches being actuated by electromagnets 1 to l-respectively. The relay C, havmg the electromagnetm actuating winding Ca, the normally open contacts C C and C and the normally closed contacts C 0 and C is provided for the control of theelectromagnetic switches aforedescribed, while the drum controller D, which is equipped with the stationary contact fingers D to D inclusive, provides for the adjustment of the resistor to the desired resistance value.

The controller functions in the following manner:

It the lines L L are energized and it is desired to start the motor, the drum controller is moved to its first operating position, thereby completing a circuit from line L to drum finger D drum finger D through magnet winding M, to line L This causes closure of the switch Ma, and the motor is connected across the linesin series with the resistances R to lit-inclusive; Closure of magnetswitch M also closes the normally open auxiliary contact Mb, so that a second path is established from drum finger D through contact Mb, through the magnet winding M to line L Thus upon movement of the drum controller to the second position the magnet winding M is maintained through the contact M7), and upon failure of voltage in this orsucceeding positions the main switch Ma is opened and cannot close again until the drumlis returned to the first op erating position, where the maximum resistance is inserted in the motor circuit, and

' thus an excessive inrush current is avoided.

i with the motor is now 18 ohms.

The motor is started at the first operating point with a total resistance of 15' ohms in series. If it is desired to increase the speed of the motor, the control is moved to the second-operating point. This causes energizar tion of the magnet Ca and the closure of magnet Ca and thus deenergization of the switch 1,-but contact has been made with .the drum finger D and since the deenergization of Ga causes closure of contact C the electror magnet 2 is energized, causing closure of switch Qaand short circuiting of the resistance R so that the total resistance in series Further movement ofthe controller to the fourth operating position causes reencrgiza tionv of Ca and thus reclosure of switch 1a, while the magnet 2 of switch 260 is maintained through contact finger D and con tact C of relay 0, which latter contact is closed .by the reenergization of the magnet Ca. Thus the total resistance in series with the motor is reduced to 12 ohms.

Further movement of the drumcontroller to the succeeding positions will cause the en ergization of the switches 2 to 4; in suclrman ner and combination, that with each successive step the total resistance in series with the motor is decreased by one ohm, and a reversal of the drum controller will cause similar increase in the resistance. It is apparent that the only contact points on the drum cont-roller which have to open and close circuits under current are the fingers D and D the former controlling the main switch when the motor is started and the latter controlling the relay Ca, which is of relatively low current capacity, and the resultingsparking therefore is negligible. The wear onthis finger and the correspond- I ing segments is therefore slight. The circuits of the other switches which are of high capacity and the magnets of which therefore are highly inductive, is made and broken 2 on the contacts C 130 C inclusive of the relay C and not on the drum controller. As these contacts openand close the circuits of the electromagnets rapidly, the resulting arcing and wear are reduced toc-onsiderably 29. lower values than would be realized, iftho circuits were made and broken on the relatively slow moving drum. 7

7 It will thus be seen that by this arrangement I vam able to obtain a relatively large number of operating points forthe controller with a small number of resistance steps and a small number of controlling electromagnets, while at the same time I have reduced the wear on the controller due to arcing. As the. magnet switches can bev mounted near the resistor and the motor, while the master druminay be mounted in any convenient place, I have reduced the number and length of heavy conductors for the controller to a minimum, while the number of small control wires, which have to be provided for between the master drumand the electromagnetic switches at the motor, is'also reduced to a minimum.

l/Vhat I claim as new and desire to secure by Letters Patent is:

In combination, a plurality of resistance sections to be included in or excluded from a circuit, said resistance sections beingso proportioned, that the ohmic value'of each sec tion is equal-to substantially twice the ohmic value of the immediately -.preceding section, and means for commutating said sections in predetermined sequence, whereby resistance gradations of equal value corresponding in number to twice the ratio of ohmic values of the last section to the first section may be obtained, said means comprising a plurality of electromagnetically operable switches each adapted to control One of said resistance-sections, anelectroresponsive relay having contacts in circuit with the operating windings of saidyplurality of electromagnetically operable switchesand a master switch having ing energized and deenergized by said master switch according to the position of the latter to execute the selections made by said master switch in respect of said electromagnetically operable switches and to render transitions substantially instantaneous.

In witness whereof, I have hereunto subscribed my name. 7

EDWIN W. SEEGER. 

